Emulsion Crystals Research Articles

Regulation of fat crystals in water-in-oil emulsions by high-intensity ultrasound: Crystal size and tracing of droplet distribution

In this paper, two emulsion systems with high and low solid fat contents were prepared from 20 % water phase and 80 % oil phase by adjusting the palm oil/palm stearin/soybean oil ratio. Different ultrasonic power and time were used for the pretreatment of emulsion with different solid fat content, and the application characteristics of ultrasonic in W/O emulsions were explored and evaluated. Directly using high-intensity ultrasound to prepare fatty emulsions would weaken the hardness and storage modulus G' of the samples. Although ultrasound reduced the size of fat crystals in emulsions, the interaction between water droplets and fat crystals needs to be considered. After ultrasonic treatment, water droplets were difficult to immobilize on the crystal surface and thus acted as an active filler to stabilize the emulsion together with the fat crystal network. In high solid fat emulsion systems, an increase in ultrasound power (from 100 W to 200 W) could more affect the crystallization behavior of fats than an increase in ultrasound duration (from 30 s to 60 s), and the distribution of crystals and droplets was more uniform. In the low solid fat emulsion system, the texture of the sample after ultrasonic treatment was softer, and the surface was more delicate and smoother. However, the higher ultrasonic intensity (200 W) was not conducive to the preparation of the spread. Although the ultrasound with excessive intensity promoted the formation of small crystals, it would also lead to the aggregation of small crystals. These small crystals cannot form a uniform crystal network, which increases the fluidity of emulsions.

Increasing the Efficiency of Emulsion Crystallization in Stirred Vessels by Targeted Application of Shear and Surfactant

Emulsions containing crystalline dispersed phases hold significant importance in pharmaceutical, chemical, and life science industries. The industrial agitation and storage of these emulsions can prompt crystallization effects within the flow field, intersecting with the primary nucleation mechanisms. Notably, contact-mediated nucleation, in which subcooled droplets crystallize upon contact with a crystalline particle, and shear-induced crystallization due to droplet deformation, are both conceivable phenomena. This study delves into the crystallization processes of emulsions in a 1 L stirred vessel, integrating an ultrasonic probe to monitor droplet crystallization progression. By scrutinizing the influence of the flow field and of the emulsifiers stabilizing the droplets, our investigation unveils the direct impact of enhanced rotational speed on accelerating the crystallization rate, correlating with increased energy input. Furthermore, the concentration of emulsifiers is observed to positively affect the crystallization process. Significantly, this pioneering investigation marks the first evaluation of emulsion crystallization considering the overlapping nucleation mechanisms seen in industrial production of melt emulsions. The findings offer valuable insights for more systematic control strategies in emulsion crystallization processes, promising more efficient and sustainable industrial practices by enabling targeted application of shear and surfactants.

Continuous Production of NaCl Spherical Particles via Emulsion Crystallization in Microfluidic Devices

Continuous Production of NaCl Spherical Particles via Emulsion Crystallization in Microfluidic Devices

Fat crystallization and physical characteristics of mung bean protein-based frozen whipped emulsions: Effect of lipophilic surfactants and quinoa hydrolysate

Yogurt ice cream (acid frozen whipped emulsion) is a complex frozen emulsion-foam system. The study investigated the impact of three lipophilic surfactant emulsifiers [glyceryl monostearate (GMS), polyglycerol ester (PGE), and sucrose ester 970 (S970)] and quinoa hydrolysate (QH) on fat crystallization, physical properties, and morphology of frozen whipped emulsions containing fermented mung bean protein. QH serves as a sustainable and health-conscious alternative to traditional emulsifiers. pH12-shifting treatment was utilized to modulate fermentation performance of mung bean protein. Yogurt-like ice creams (10% coconut oil) were formulated using pre-whipped emulsions comprising fermented pH12-treated mung bean protein (FMP12) or native mung bean protein (NFMP), along with 0.5% (w/w) emulsifiers or QH. Pre-whipped FMP12 emulsions exhibited significantly higher emulsification stability (P < 0.05) compared to NFMP emulsions, owing to the better-balanced hydrophilic-lipophilic nature of FMP12. The individual addition of surfactants and QH promoted fat crystallization and improved the stability and viscous of FMP12 emulsion by competitively adsorbing with FMP12 at the O/W interface. Upon freezing, all three surfactants in whipped creams resulted in uniform and fine ice crystals with a moderate accumulation of oil droplets, showing a comparable effect to QH. Consequently, FMP12 frozen whipped emulsions with surfactants or QH both exhibited superior hardness and overrun, attributed to the presence of fine ice crystals and a stable fat crystal skeleton structure. These findings indicate the prospective utility of QH as a substitute for conventional small chemical emulsifiers, thereby enhancing the quality attributes of plant-based yogurt ice cream.

Network Structure and Nanoplatelet Characterization of the Edible Fat Crystallization in Low-Fat W/O Emulsions.

Fat crystals provided the strength of the colloidal network in W/O emulsions and stabilized water droplets. To understand the stabilizing effect of fat-regulated emulsions, W/O emulsions with different edible fats were fabricated. The result indicated that more stable W/O emulsions were produced by palm oil (PO) and palm stearin (PS), whose proportions of fatty acids were similar. Meanwhile, water droplets inhibited the crystallization of emulsified fats but participated in the formation of the colloidal network with fat crystals in emulsions, and the Avrami equation showed a slower crystallization rate of emulsified fats than the corresponding fat blends. However, water droplets participated in the formation of a colloidal network of fat crystals in emulsions, and the adjacent fat crystals were connected through a bridge constructed by water droplets. Fats in the emulsion containing palm stearin crystallized faster and more easily formed the β-polymorph. The small-angle X-ray scattering (SAXS) data were interpreted by the unified fit model to determine the average size of crystalline nanoplatelets (CNPs). The larger CNPs (>100 nm) with a rough surface of emulsified fats and a uniform distribution of their aggregates was confirmed.

Enhancing Protein Crystal Nucleation Using In Situ Templating on Bioconjugate-Functionalized Nanoparticles and Machine Learning.

Although protein crystallization offers a promising alternative to chromatography for lower-cost protein purification, slow nucleation kinetics and high protein concentration requirements are major barriers for using crystallization as a viable strategy in downstream protein purification. Here, we demonstrate that nanoparticles functionalized with bioconjugates can result in an in situ template for inducing rapid crystallization of proteins at low protein concentration conditions. We use a microbatch crystallization setup to show that the range of successful crystallization conditions is expanded by the presence of functionalized nanoparticles. Furthermore, we use a custom machine learning-enabled emulsion crystallization setup to rigorously quantify nucleation parameters. We show that bioconjugate-functionalized nanoparticles can result in up to a 7-fold decrease in the induction time and a 3-fold increase in the nucleation rate of model proteins compared to those in control environments. We thus provide foundational insight that could enable crystallization to be used in protein manufacturing by reducing both the protein concentration and the time required to nucleate protein crystals.

Tracing distribution and interface behavior of water droplets in W/O emulsions with fat crystals

Sucrose palmitate (P170) and sucrose laurate (L195) were used as emulsifiers to control the crystallization behavior of AMF and to stabilize W/O emulsions. In this study, the P170 promoted crystallization and led to strong fat crystal networks with smaller AMF crystals (60–80 μm) in emulsions, retaining flocculation. Water droplets were squeezed into irregular shapes between the strong network but the P170 formed an interface layer with better strength to resist the aggregation. Contrarily, the L195 inhibited crystallization and formed larger AMF spherulites (more than 100 μm) resulting in a low strength of fat crystal networks and unstable emulsions. Meanwhile, the water droplets were easily fixed on the surface of AMF crystals because of the existence of sucrose esters. Protruding crystals on the surface of larger spherulites could pierce the water-oil interface, leading to a greater coalescence and forming larger water droplets. Therefore, a weak crystal network could not prevent the sedimentation and phase separation caused by gravity.

Investigation of the surfactant distribution in oil-in-water emulsions during the crystallization of the dispersed phase via nuclear magnetic resonance relaxometry and diffusometry.

The crystallization of melt emulsions is of great interest to the food, cosmetic, and pharmaceutical industries. Surfactants are used in emulsions and suspensions to stabilize the dispersed phase; thus, questions arise about the liquid-liquid and solid-liquid interfaces of the droplets or particles and the distribution of the surfactant in the different phases (continuous and dispersed phase, interface). Nuclear magnetic resonance relaxation and diffusion measurements revealed that the internal and rotational mobility of surfactant molecules at the liquid-liquid interface decreases with increasing droplet sizes. Additionally, solid-liquid interfaces have fewer surfactants than liquid-liquid interfaces as a result of the desorption of the surfactant molecules during the crystallization of the droplets. Relaxation rates of surfactant molecules in aqueous solution as single molecules, micelles, and at the liquid-liquid and solid-liquid interface are analyzed for the first time.

The interfacial digestion behavior of crystalline oil-in-water emulsions stabilized by sodium caseinate during in vitro gastrointestinal digestion

The interfacial digestion behavior of crystalline oil-in-water (O/W) emulsions was studied using sodium caseinate-stabilized 4% and 20% palm stearin-in-water emulsions (4% PS and 20% PS) with 4% and 20% palm olein-in-water emulsions as control. Variations in fat crystal form and microstructure, interfacial adsorbed protein percentage and concentration, and rheological properties during in vitro gastrointestinal digestion and intestinal lipid digestion behavior were determined. Initially, fat crystals in both PS-based emulsions were dominated by β′ polymorph. After gastric digestion, the β′-to-β transition was observed and both PS-based emulsions mainly contained β crystals, but 20% PS had a higher β crystal content (∼85% vs. 60%, p < 0.001) and viscosity than 4% PS. These β crystals induced in the gastric phase with large size, dense packing, and a high onset melting temperature (46.8 ± 0.2 °C) probably played a major role in slowing down lipid digestion, as confirmed by a greater extent of decreased lipolysis rate of 20% PS (∼37%) than 4% PS (∼10%) at the initial stage of intestinal digestion. The lipolysis extent of PS-based emulsions is strongly dependent on their solid fat content (SFC). The digestion extent of 4% PS was not affected by its low SFC (2.6%), while a high SFC of 20% PS (12.5%) promoted its lipolysis as fat crystals in it adsorbed at the oil-water interface to facilitate the formation of stable spherical droplets. This study highlighted the crucial role of gastric rather than initial fat crystal polymorph in impacting lipid digestion rate of protein-stabilized O/W emulsions.

Porous Crystalsomes via Emulsion Crystallization and Polymer Phase Separation.

Crystalsomes are crystalline capsules that are formed by controlling polymer crystallization to break translational symmetry. While recent studies showed that these crystalline capsules exhibit interesting mechanical properties, thermal behavior, and excellent performance in blood circulation, the closed capsule is undesired for drug delivery applications. We report the formation and characterization of porous crystalsomes where porosity is rendered on the crystalline shells. A miniemulsion is formed using two amphiphilic block copolymers (BCP). The competition between controlled crystallization and phase separation of the BCPs at the emulsion surface leads to multiphase crystalsomes. Subsequently removing one BCP produces porous crystalline capsules.

Integrated membrane emulsification and solution cooling crystallization to obtain a narrow and predictable crystal size distribution

• A novel concept integrating membrane emulsification and solution crystallization. • Membrane emulsification enabled the confinement of solution crystallization. • Different droplet size distributions showed different yield and crystal quality. • A narrow crystal size distribution was achieved through monodisperse droplets. • The crystal number density was affected both by supersaturation and droplet size. Solution crystallization processes are challenged by the need to control crystal quality attributes such as the crystal size distribution (CSD). Emulsion crystallization is an attractive process intensification strategy to control crystal quality attributes through miniaturization. Droplets of an emulsion can act as tiny crystallizers by confining crystals so that crystal nucleation and growth are limited by the droplet size with available supersaturation. This work presents a novel process concept based on the integration of membrane emulsification and solution crystallization. A water-in-oil emulsion is created through membrane emulsification and glycine is crystallized inside droplets by cooling. The process is characterized in terms of the droplet size distribution, crystal number density, and CSD as a function of the emulsification method and supersaturation. Large and monodisperse droplets obtained from membrane emulsification can achieve a narrow and predictable CSD with higher productivity compared to a mechanical emulsification method. The crystal number density is strongly affected by the initial supersaturation when using membrane emulsification but not the final CSD. In contrast, the CSD changes with supersaturation when applying a mechanical emulsification method. The CSD obtained from a conventional bulk crystallization process is broader and lacks the control imposed by the uniform droplets from membrane emulsification.

Ultrasound-modified interfacial properties and crystallization behavior of aerated emulsions fabricated with pH-shifting treated pea protein

The interfacial properties of pea protein isolate (NPP) were modified by pH12-shifting (BPP) and ultrasound treatment as a substitute for skimmed milk powder (SMP) in ice cream. The physicochemical properties and fat crystallization in emulsions before and after whipping were analyzed. Compared with SMP, the BPP emulsion displayed superior stability with small particle size and high viscosity. Fat clusters were observed in both SMP and BPP emulsions, which may promote the puncture and protrusion of fat crystals within droplets and lead to partial coalescence to allow air bubble entrapment. Aeration activity of BPP in cream was 1.5-fold that of NPP. Although the overrun value was smaller than SMP cream, the BPP cream retained the stable shape and had a slow melting rate due to its interactive dimensional network of fat. Ultrasound treatment was found to promote fat crystallization of emulsions, leading to the improved stability of final products.

Melt Crystallization of Ammonium Dinitramide (ADN) Investigated by Means of X‐ray Diffraction

AbstractAmmonium dinitramide (ADN) is a promising oxidizing agent for solid rocket propellants. In situ XRD investigations of ADN and ADN suspensions have been performed in order to understand and refine the emulsion crystallization process for manufacturing spherical ADN particles (prills). The investigation revealed that the melt crystallization behavior depends on ADN quality, humidity, maximum temperature of temperature cycles, and suspension agents. Further investigations will focus on additives for controlling the mechanisms investigated, e.g., by seeding.

Influence of Shear Flow on the Crystallization of Organic Melt Emulsions – A Rheo‐Nuclear Magnetic Resonance Investigation

AbstractThere is a need to better understand the influence of shear flow on the crystallization of a molten oil phase in an oil/water emulsion due to its high relevance for industrial processes. The present study focuses on the influence of laminar shear flow on the crystallization kinetics of polydisperse n‐hexadecane‐in‐water emulsions. The investigation was carried out by rheo‐nuclear magnetic resonance (NMR) spectroscopy in a Taylor‐Couette geometry. An accelerating impact of the shear rate on the overall crystallization kinetics was verified. This effect stems from an increase of the collision frequency of already crystallized droplets with not yet crystallized droplets. Nevertheless, the collision efficiency decreased with higher shear rate.

Effect of electromagnetic field on water-in-oil emulsion and calcium carbonate crystallization

The investigation was devoted to the effect of electromagnetic field on crystallization of calcium carbonate, structure of CaCO3 crystals generated from oversaturated aqueous solutions, and water-in-oil emulsion (crude oil) properties. XRD demonstrated that electromagnetic field caused a decrease in mean size of CaCO3 particles by 30 μm and prevalent aragonite formation. We detected that electromagnetic field application leads to decreased apparent viscosity of water-in-oil emulsion and inhibits influence of a non-ionogenic surfactant on stability and viscosity properties of crude oil. As a matter of practice, the method demonstrated its efficiency to prevent scale deposits in oil production wells.

ADN Recrystallization and Microencapsulation with HTPB by Simple Coacervation

AbstractAmmonium dinitramide (ADN) has been considered the potential substitute for ammonium perchlorate in solid green propellants. However, it has also some drawbacks due to its high hygroscopicity and chemical incompatibility with some of the components present in composite propellant formulations. On the other hand, ADN melts at temperatures below degradation, which makes emulsion crystallization an important method to prepare spherical ADN particles that benefit both propellant slurry processing and casting. Spherical ADN particles were prepared by emulsion crystallization to be used for the microencapsulation studies, and whose method was assessed to better understand which parameters may affect the ADN particles formation. Microencapsulation protects ADN particles as it addresses hygroscopicity besides the given protection from chemical incompatibility. Polyurethane made of hydroxyl‐terminated polybutadiene was selected as a coating material because of its common use in propellants as a binder. Also, the good performance of methylene diphenyl diisocyanate as a curing agent was such that it was used in the whole study. The number of layers and the processing time played important roles in the formation of the capsule as seen in the impermeability tests. Besides, drying at 50 °C for 168 h showed to be even more beneficial on average for the capsule protective property. Chemical compatibility between the capsule and ADN was confirmed at 60 °C which allows it to be used as a protective coating. However, the obtained average coating thickness of ten microns has to be reduced yet with more efficient protective coating materials.

Effect of emulsifier-fat interactions and interfacial competitive adsorption of emulsifiers with proteins on fat crystallization and stability of whipped-frozen emulsions

Fat crystals and adsorbed interfacial layer are very important in controlling the stability of partly crystalline fat globules. In this study, the effects of competitive adsorption of emulsifiers, including glyceryl monooleate (GMO) and sucrose ester (SE) with milk proteins and emulsifier-fat (anhydrous milk fat, AMF; coconut oil, CO) interactions on the fat crystallization behavior and stability of whipped-frozen emulsions were investigated. Parameters such as zeta potential, surface protein coverage, rheological property, fat crystallization behavior, overrun, melting rate and microstructure of ice cream were determined. The results indicated both GMO and SE affected the crystallization behavior, changing the crystal growth, morphology and stiffness. Different mechanism was involved in fat partial coalescence in emulsion systems with different fat-emulsifier interactions. The promotion of partial coalescence in whipped-frozen emulsions with increasing concentration of GMO was mainly related to fat crystallization behavior combined with increased fat crystal growth dimension and protrusion length at the fat globule surface, since protein surface coverage was not affected by GMO concentration. However, in the case of emulsions with SE, enhancement of partial coalescence was mainly related to decreased protein surface coverage combined with less resistance of interfacial membranes to penetration by small fat crystals. Ice cream based on CO were distinguished by higher overruns and lower melting rates compared to ice cream based on AMF with the same levels of emulsifiers, especially strong fat crystal network in the presence of GMO accounts for the increased air bubble stability. These findings provides a theoretical basis for aerated food processing.

Ultrasound-mediated interfacial protein adsorption and fat crystallization in cholesterol-reduced lard emulsion.

Lard with a substantially reduced cholesterol content through aqueous enzyme extraction is an attractive source of lipid in healthy and nutritious emulsion food product development. The objective of this study was to elucidate the crystallization behavior (4-20 °C) of emulsions prepared from low-cholesterol lard in relation to protein emulsifier (2 and 4% whey protein isolate, WPI) and ultrasound (475 w, 5 min) treatments. The physicochemical properties and fat crystallization pattern of the emulsions were investigated. Emulsions with 4% WPI were superior to those with 2% WPI on interfacial adsorption and crystal size reduction. Ultrasonic treatment of prepared emulsions further decreased fat crystal size, promoted small and uniform crystal distribution, and slightly destabilized emulsions. Protein concentration and ultrasonic treatment had no obvious effect on crystal transition from β' to the more stable β-form based on X-ray diffraction. The melting properties determined by differential scanning calorimetry indicated that emulsified lard had a lower onset melting temperature than bulk lard, and with ultrasound treatment, the melting enthalpy increased remarkably. The ultrasound-induced change in fat crystalline structure and emulsion meta-stability may be valuable to the manufacture of healthy, emulsion-incorporated food products.

Properties and Structure of ADN‐Prills

AbstractAmmonium dinitramide (ADN) is the upcoming oxidizer for solid propellants of the current decade. Spherical ADN particles, so‐called ADN‐prills, are a key product for the development of environmentally friendly and low‐signature solid propellants for defence and space applications. At the moment the particle size and the spherical shape of the ADN‐prills can be controlled by the emulsion crystallization process or by spray congealing processes. In this work the crystal structure and the thermal‐ and mechanical stability of ADN‐prills were investigated. By temperature resolved X‐ray diffraction measurements new insights about temperature depending crystalline structures inside of ADN‐prills could be gained. Anisotropic crystal properties could be detected at certain temperature ranges between ambient temperature and the melting point of ADN at 93 °C. Due to the unexpected material properties of molten ADN droplets a surprising correlation between process parameters, particle size, crystal structure, thermal stability and mechanical stability was found. This leads to a more profound knowledge about the crystal structure of ADN‐prills and gives the opportunity to produce enhanced ADN particles for propellant applications.

A Novel Spherulitic Self-Assembly Strategy for Organic Explosives: Modifying the Hydrogen Bonds by Polymeric Additives in Emulsion Crystallization

A novel strategy to prepare spherical crystals of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) has been developed by introducing polymeric additives into the antisolvent emulsion crystallization. The spherical crystals are induced by modifying the intermolecular hydrogen bonds network of LLM-105. The results show that the concentration of polyvinylpyrrolidone (PVP), which acts as a polymeric additive, is a crucial factor to get quite different morphologies of LLM-105 crystal products. X-like shaped crystals have been produced in the absence of PVP. In contrast, spherical crystals have been obtained in the presence of PVP. Importantly, LLM-105 spherulites with a mean particle size of 78.0 μm can be obtained by adding a proper amount of PVP, which has a narrow size distribution (CV = 31.2). In addition, time-resolved morphological evolution processes of X-like shaped and spherical crystals have been performed. Meanwhile, 1H NMR experiments also have been conducted to understand the intermolecular hydrogen bonds between LLM-105 molecules and the polymer. Inspired by the result of the above experiments, an LLM-105 spherulitic formation mechanism has been proposed. Furthermore, LLM-105 spherulites exhibit more excellent mechanical and safety properties. It is suggested that these spherulites have a great potentiality in the military application. Therefore, this polymer-induced spherical crystallization method is significantly important for the design and fabrication of organic small molecules with spherical shapes.